1. Field of the Invention
The present invention is related to a sports boot of the front entry type with variable volume having a shell constituted of an upper and a shell base that overlap each other at least partially and that are connected to each other in a pivoting manner; it is also related to a bending mechanism adapted to determine the flexibility characteristics of the upper relative to the shell base.
2. Description of Background and Relevant Information
In known boots of this type, such as the ski boots disclosed in the European patent applications EP 666 036 and EP 671 133, the European patent EP 350 023 and the German Utility Model G 92 17 787.5, the overlapping zone of the upper with the shell base extends approximately along the entire area corresponding to the user's ankle for obvious sealing reasons. More specifically, in the dorsal zone of the boot, the shell base has a more or less thin and flexible vertical extension originating in one piece with its wall, which is nested beneath the lower border of the upper. This vertical extension, which forms the equivalent of a half tube, is slit via a vertical notch, open upwardly, whose demarcating edges extend freely beneath the upper, and at a level located above the pivot axes thereof. By these arrangements, when the upper pivots towards the front, the slit part of the vertical extension can becomes deformed elastically without being buttressed and thus accompany the upper that overlaps it in its movements.
As has been taught, the pivoting of the upper is thus made possible as long as the elastic resistance of the vertical extension, and thus of its slit portion, can be overcome, which implies a relative coming together of the opposing edges demarcating the notch. The bending capacity of the vertical extension consequently determines the flexibility characteristics during the bending of the boot. However, because the vertical extension is made in one piece with the shell base, it is the type of material constituting the shell base that actually determines whether the boot will be more or less flexible, i.e., that imparts it with its initial flexibility.
In view of the fact that the shell base of these types of boots, as is the case with most "variable volume" boots, must be adjusted on the foot by means of tightening devices that adjust the effect of its enveloping, the known solution for obtaining an adapted optimum initial flexibility for each relevant portion of the boot thus consists of varying the thickness of the wall of the shell base, which is made from a given material, most often plastic. To this end, the wall is designed to be thin in the region of the closure flaps of the shell base, and clearly thicker in the region of the slit portion of the vertical extension, as well as in the lower region that extends down to the walking sole.
This design for boots with variable volume enables reaching a good stiffness-flexibility compromise for a given design of boot, as long as the plastic material selected is not too stiff, because in this case it would be necessary to obtain extremely thin walls, perhaps even excessively thin walls, in the areas of the tightening devices, i.e., in areas where the shell base has to be adjusted on the user's foot, as, for example, in the instep zone. In fact, almost always, it is a relatively flexible material that is usually used, which enables defining the various regions of the shell base into wall thicknesses that remain compatible with traditional plastic molding methods, even if there is a need to increase the thickness of the most biased areas.
The boots designed in this manner, i.e., with an increased thickness of the wall especially on the slit portion of the vertical extensions, definitely provide a measure of satisfaction as regards functionality because the flexibility of the upper results from a pulling effect on the dorsal zone of the shell base without any blocking during the entire period that the opposite edges of the notch remain free to come closer together. In addition, by proceeding in this manner, the force that the user applies on the upper is distributed over a large enveloping surface, extending along the entire lower frontal zone of the leg, which means that substantial localized pressures can be avoided. However, this boot design has the disadvantage of making them considerably heavier, and it also does not allow for the development of a base structure that can be common or standard for several boot designs wherein varying initial flexibility characteristics are desired. Indeed, with this object in mind, it becomes necessary to obtain a specific shell base for each design, or even for each level of initial flexibility desired, by varying the choice of the plastic material used and/or by varying the thickness of its walls.
Obviously, it is known to attach and/or associate to the bending slit of the shell base, adjustment devices intended to modify the initial flexibility characteristics that the slit is capable of providing for a given boot design. This is the main focus of the documents EP 666 036, EP 671 133, EP 350 023 and DE G 92 17 787.5 cited previously.
More specifically, the adjustment devices of the boots described in the European documents EP 350 023, EP 666 036, and EP 671 133, act on the opposite edges of the vertical extension notch originating from the shell base, whereas the one from the boot described in the German document G 92 17 787.5 acts directly between the upper and the shell base. Thus, the initial flexibility of the upper can be modified and controlled very easily, both in terms of force as well as in terms of amplitude, by simply varying the value of the space left free between the opposite edges of the notch and/or the height of the notch that is allowed to bend. Obviously, the latter adjustment simultaneously causes a change in the level of the forces to be generated because it modifies the height of the support taken by the upper on the slit portion of the vertical extension with respect to the connecting and pivot axes of the upper. However, it is apparent from these boot constructions that obtaining the vertical slit extension all in one piece with the shell base, once again adversely impacts these types of boots. Indeed, by acting directly, for example, on the edges of the notch with the adjustment devices taught by the documents EP 350 023, EP 666 036 and EP 671 133, the stresses, especially the pressures, are very high in the area of the contact points with the adjustable abutments of these devices, and that they cause a rapid deterioration of the edges of the notch. This deterioration is a result of the fact that the available support surface is limited to the surface offered by the wall thickness of the vertical extension in the area of the notch, and to the surface offered by the ends of the adjustable abutments. Another reason is the fact that the elastic material constituting the vertical extension is the same as that of the shell base, i.e., relatively flexible so as to allow a good stiffness-flexibility compromise, whilst remaining compatible with the traditional molding methods of plastic materials.
Obviously, in the case of the adjustment device taught by the German document G 92 17 787.5, the above-cited disadvantage does not manifest itself because this adjustment device acts directly between the upper and the shell base by using a tension adjustable spring. However, this device extends along the dorsal zone of the boot and, consequently, has a substantial encumbrance in this zone, which must often be relatively clear so as to provide space for the binding and/or affixing systems of the boot on sports devices, such as skis, for example. In addition, this device is relatively complex because it makes use of numerous mechanical elements.
It is clear that regardless of the adjustment devices that are implemented on this type of boot, they are only efficient in the sense that they make the boot less flexible than it was initially by reducing the frontward bending ability of its upper and/or by increasing the level of forces that can be generated on the latter in order to cause it to bend. The adjustment devices of the boots disclosed hereinabove thus necessarily have to provide a specific shell base and/or an "upper-shell base" structure for each boot design, i.e., specific to each level of initial flexibility desired.